The present invention relates to the field of autoalignment systems for high power lasers and more particularly to autoalignment systems utilizing a separate alignment laser. In even greater particularity, the present invention relates to autoalignment systems for high power lasers capable of cavity mode control and beam pointing stabilization.
In many potential high power laser applications it is necessary to control the direction of output beam propagation to within a few micro-radians. Consequently, the development of highly accurate autoalignment systems for such lasers is of current interest. The extremely high power levels of high power lasers preclude the use of ordinary optical techniques employing such optical components as beam splitters and optical windows. Beyond this threshold constraint, the use of an unstable resonator cavity to generate the laser beam involves an additional consideration, namely mode control. Thus, in addition to maintaining the alignment of the mirrors of the laser train which point the output beam, an autoalignment system for a laser utilizing an unstable resonator cavity must be capable of establishing cavity mode control. In other words, two separate alignment functions must be accommodated by an autoalignment system for such a laser
A further object of the present invention is to provide an autoalignment system which can provide both pointing stabilization for the output beam and mode control for the unstable resonator cavity.
Another object of the present invention is to provide an autoalignment system which utilizes a single, separate HeNe laser to provide an alignment beam coupled to and directed along the high power laser train.
Still another object of the present invention is to provide an autoalignment system in which only detector packages or secondary optical elements are placed on the main laser mirrors.
Yet another object of the present invention is to provide an autoalignment system of the character described in which detected displacements of an alignment beam can be translated into compensating tilt adjustments to the controlled mirrors of the high power laser train.
Accordingly, to accomplish these and other objects, the present invention provides a method and system for automatically aligning a high power laser. The high power laser train includes an integral unstable resonator oscillator for generating the laser beam and two turning mirrors to point the beam. The unstable resonator cavity is defined by two end mirror configurations: a concave end mirror and a combination convex/coupling end mirror. The convex/coupling mirror comprises the integral combination of a central convex mirror circumscribed by a flat, annular, coupling mirror. The laser beam generated between the concave and the convex mirrors of the resonator cavity is coupled out of the cavity by means of the coupling mirror, being reflected configuration, pointing stabilization for the output laser beam and mode control for the unstable resonator cavity.
One technique suggested for automatically aligning high power laser systems entails the use of a separate, usually HeNe (helium/neon), laser to provide a low-power alignment beam. The alignment beam is coupled to and directed along the optical train of the high power laser, propagating through all the relay optics of the main laser apparatus. A straight forward method of implementing this autoalignment technique in a gas dynamic laser apparatus utilizing an unstable resonator cavity would be to use two autoalignment systems. One would be used to control and adjust the mirrors directing the pointing of the output laser beam; the other would be used to establish mode control for the resonator cavity. However, because of the frequency-response requirements of dynamic mirror mounts and the geometric constraints resulting from the requirements of low-pressure optical boxes for the gas dynamic laser train, it is not feasible to place the autoalignment system directly on the mirror mounts. These frequency response requirements and geometric constraints necessitate that the structural components of an autoalignment system placed directly on the main laser mirrors be limited to detector packages and secondary optical elements.